1. Technical Field
The present application relates to a fin used to generate propulsion and control forces for a vehicle in an underwater or water surface environment. More particularly, the instant application discloses a propulsion fin which can actively change its curvature during flapping stroke cycles and thus provides a single mechanism through which directional control over propulsive forces can be achieved.
2. Related Technology
The subject matter of this patent application disclosure has wide application to maritime propulsion, steering and direction control systems for underwater vehicles and vehicles which traverse surface waters.
Known methods of force production for propulsion and control of underwater and surface vehicles use rotating propellers, and/or rigid or passively deforming fins.
There are many undersea areas in which traditional propulsion and sensing techniques have proven effective for unmanned systems, but such undersea areas have mostly been in open waters.
Rotating propellers have limitations in force production at slow speeds and in highly dynamic environments where water flows are constantly changing. Additionally, a propeller on its own can only be used to propel a vehicle. It would require multiple non-coaxial propellers or a system of control surfaces for steering and directional control. Propellers also have disadvantages in certain environments as they are noisy, and can be adversely affected by interference of debris, such as near-shore vegetation.
Researchers seeking to improve on vehicle performance in cluttered undersea areas with fast changing currents and near-surface wave effects draw inspiration from fish and other aquatic organisms which inhabit these types of environments, where unmanned platforms could prove to be very useful. Combinations of finned propulsion and control surface actuation, and unique sensory systems provide these organisms the abilities they need to survive and thrive.
According to J. E. Colgate et al. “Mechanics and control of swimming: a review,” IEEE Journal of Oceanic Engineering, vol. 29, pp. 660-673, July 2004 and J. C. Liao, “A review of fish swimming mechanics and behavior in altered flows,” Philosophical Transactions of the Royal Society B. vol. 362(1487), pp. 1973-1993, November 2007, a number of researchers have studied the fin force production mechanisms of fish. Several investigators have developed and adapted rigid and passively deforming robotic pectoral fins onto unmanned underwater vehicles (UUV's) including B. Hobson, et al. “PilotFish: Maximizing agility in an unmanned underwater vehicle,” Proceedings of the International Symposium on Unmanned Untethered Submersible Technology, Durham, N.H., 1999; S. Licht, et al. “Design and projected performance of a flapping foil AUV,” IEEE Journal of Oceanic Engineering, vol. 29, no. 3, 2004; P. Sitorus, et al. “Design and implementation of paired pectoral fins locomotion of labriform fish applied to a fish robot,” Journal of Bionic Engineering, vol. 6, pp. 37-45, 2009; and N. Kato, et al., “Elastic pectoral fin actuators for biomimetic underwater vehicles,” in Bio-mechanisms of Swimming and Flying, chap. 9, Springer Japan, 2008, pp. 271-282.
Other investigators have sought to develop actively controlled curvature pectoral fins including N. Kato, et al., “Elastic pectoral fin actuators for biomimetic underwater vehicles,” in Bio-mechanisms of Swimming and Flying, chap. 9, Springer Japan, 2008, pp. 271-282; J. Palmisano, et al., “Design of a biomimetic controlled-curvature robotic pectoral fin,” IEEE International Conference on Robotics and Automation, Rome, Itlay, 2007; K. W. Moored et al., “Investigating the thrust production of a myliobatoid-inspired oscillating wing,” 3rd International CIMTEC Conference, Acireal, Italy, Jun. 8-13, 2008; and J. Tangorra et al., “The effect of fin ray flexural ridgidity on the propulsive forces generated by a biorobetic fish pectoral fin,” The Journal of Experimental Biology, vol. 213, pp. 4043-4054, 2010.
Thus, rigid and passively deforming fins have a limitation in force production control, as there are fewer degrees of freedom which can be actuated, and thus less control over the direction of force production. Further, passively deforming fins generally require a trial-and-error method of determining shape deformation under loads.
A fin that can actively change its curvature during flapping stroke cycles provides a single mechanism through which directional control and through which propulsive forces can be achieved simultaneously. The instant invention provides a fin having an effector of propulsion and control that will not be damaged when operating in vegetation or other debris, such as in near shore environments where precise low-speed maneuvering is needed. It also enables greater control in flow-changing environments than traditional propellers and rigid/passive fins as the fin surface shape can be changed to take advantage of data involving a multitude of flow conditions. Therefore, the need exists for a fin that can actively change its curvature during flapping stroke cycles. Further, the need exists for a fin which provides a single mechanism through which directional control over propulsive forces can be achieved. In addition, the need exists for a fin which also provides an effector of propulsion and control that will not be damaged when operating in vegetation or other debris. Finally, the need exists for a fin which enables greater control in flow-changing environments contrasted with traditional propellers and rigid/passive fins as the fin surface shape can be changed to take advantage of a multitude of flow conditions.